The desirability of removing sulfur compounds from gaseous streams for various reasons has been long recognized. Activated carbon has often been used to remove sulfur compounds such as H.sub.2 S from natural and manufactured gases, ammonia, hydrogen and LPG. Recently it has become desirable to remove substantially all sulfur compounds from the hydrogen recycle stream used in hydrocarbon reforming systems. Modern bimetallic reforming catalysts require low-sulfur conditions for efficient operation.
This invention is directed to regenerating a solid reactant of copper-chromium on a high-surface-area carbon support, when the reactive sulfur removal capacity of the reactant has been used up by reaction with hydrogen sulfide. The invention affords a substantially complete regeneration of the solid reactant and, at the same time, induces little or no change to the porous carbon support from oxidation or sintering. This invention has particular utility in regenerating solid reactants which have become expended in removing hydrogen sulfide from recycle hydrogen in reforming systems in which very low recycle hydrogen gas sulfur levels (as low as tenths of a ppm) are desired, allowing the regenerated reactant to be reused in scrubbing sulfur compounds from the recycle hydrogen stream.
A number of processes have been disclosed for removing sulfur compounds from gaseous streams. U.S. Pat. No. 3,382,044 teaches the use of zinc oxide to adsorb hydrogen sulfide. U.S. Pat. No. 3,398,509 teaches the use of carbon to adsorb SO.sub.2 and heating the carbon in an inert gas to desorb the SO.sub.2. U.S. Pat. No. 3,416,293 teaches removing the sulfur compounds from industrial gas streams by adsorption on a bed of activated carbon modified by the addition of a metal selected from copper, iron, manganese, nickel, cobalt, cadmium and zinc, and a process for regenerating the adsorbent with steam.
U.S. Pat. No. 3,501,897 teaches a cyclic regenerative process for removing sulfur oxides from flue gas by means of a solid acceptor which may be copper oxide, wherein the regeneration of the solid acceptor is carried out by passing a reducing gas through it at a temperature from about 300.degree.-500.degree. C. The base material must be capable of withstanding the temperatures used for the removal of the sulfur oxides. Suitable materials are alumina, silica, silica-alumina, and/or silica-magnesia.
Pages 66-70 of the Aug. 31, 1972 Oil & Gas Journal discuss the regeneration of a copper oxide adsorbent used for scrubbing SO.sub.2.
U.S. Pat. No. 3,739,550 teaches regeneration of carbonaceous adsorbents containing vanadium, lithium, aluminum or chromium and phosphorus with nitrogen at 600.degree. C.
U.S. Pat. No. 2,747,968 describes regeneration of a copper, nickel or cadmium component which may be supported on a carrier such as alumina or silica and may be promoted with chromic acid, nickel oxide or nickel sulfide. Regeneration is effected at 350.degree.-850.degree. C (about 660.degree.-1560.degree. F) by first passing a slow stream of an oxidizing gas such as air over the reactant followed by a slow stream of a reducing gas, after the reactant has become expended by contact with hydrogen sulfide-containing gases.
U.S. Pat. No. 1,947,776 describes regeneration of a reactant containing, e.g., copper and chromium on, e.g., pumice or firebrick, by passing air over the reactant at an elevated temperature, e.g., 840.degree. F.
U.S. Pat. No. 3,576,596 describes removal of carbon monoxide and nitric oxide from gases using a mixture of copper and chromium on activated carbon.
U.S. Pat. No. 3,883,637 describes removing odorous sulfur compounds from air using a mixture of copper and chromium on activated charcoal.
The process of the present invention provides an effective way of regenerating a solid reactant which has become expended by reaction with hydrogen sulfide in a hydrogen recycle gas stream when the reactant is comprised in part of porous carbon, in a manner which prevents sintering or oxidation and concomitant destruction of the reactant and also allows the reactant to be reused for removing sulfur from the hydrogen recycle gas to provide a substantially sulfur-free recycle stream.